In the field of transient tolerance tests, few studies have been conducted on gate voltage spikes of GaN HEMT components. A parametric generation of such overvoltage either implies precise and tedious hardware gate circuitry design, or require some simplification of the waveform making it less representative of actual and practical cases. Such tests will be easier to conduct thanks to the original 50 Ohms environment setup proposed in this work. This original test bench improves usual measurement bandwidths. It also allows spatial isolation of a tested device with its driver and power circuits (e.g. over one meter), limiting their complex interactions. As a first demonstration of the setup capability, the breakdown overvoltage of a p-GaN HEMT is determined. Several gate voltage overshoots as high as twice the DUT nominal rating are then demonstrated not to degrade the tested device. Moreover, allowing such overshoots may enable to significantly reduce switching losses.